The invention relates to a locking head for a crane jib comprising at least two telescope sections.
In the case of larger cranes and mobile cranes with telescopic jibs, the individual telescope sections of the jib are usually moved relative to one another by means of a telescoping device in order to extend and retract the jib in a telescoping movement. Such cranes with a telescopic jib and a locking head are already known from EP 0 943 580 B1 and EP 1 153 875 B1. On the end at which the piston rod extends out from the cylinder, the telescoping device used for this purpose has a locking head which can be moved by the telescoping device in the longitudinal direction of the jib and essentially fulfils two functions. Firstly, before extending or retracting the respective telescope sections, the lock between the telescope section to be moved and the next outer telescope section has to be released and locked again at another point after the extending or retracting operation. Secondly, the telescope section which has to be moved has to be coupled respectively with the locking head and hence with the telescoping device so that an extending or retracting movement of the telescoping device causes an extending or retracting movement of the respective telescope section. In this respect, it is necessary to ensure that the respective telescope section is coupled with the locking head before the lock with the next outer telescope section is released and that it is not uncoupled from the locking head again until the lock with the next outer telescope section has been established.
EP 0 754 646 B1 discloses a locking head, whereby in order to increase operating safety, hydraulic circuits are controlled by drivers positioned by the locking bolts to be moved so that the telescope sections cannot be unlocked until the drivers have been positioned on the telescope section to be moved and conversely, the drivers cannot be released from the telescope section to be moved until the lock between two telescope sections has been established again.
DE 100 04 838 discloses a locking head, whereby the locking head is coupled by means of a first hydraulic cylinder and the lock between the individual telescope sections is operated by means of a second hydraulic cylinder. As a result, different power sources are provided for the coupling device and the locking device.
DE 198 24 672 discloses a locking head which is provided in the form of a bush and is displaceable on the cylinder housing of a piston-cylinder unit. A piece with two guide grooves which can be displaced relative to the locking head is provided as a means of operating locking bolts, and a guide ring disposed perpendicular to it and which engages in another guide groove is provided as a means of operating a telescope section lock.